Certain vehicles, such as diesel-electric locomotives and diesel-electric off-highway mining trucks, are powered by electric fraction motors powered by, for example, alternating current generated by an alternating current (AC) alternator-rectifier or a direct current (DC) generator, that in turn is powered by a diesel engine. Such diesel-electric vehicles commonly use dynamic braking systems. In dynamic braking systems, the armature of each traction motor is connected across a forced-air-cooled resistance grid, known as a dynamic braking grid, which typically is located in the engine compartment of a locomotive or other vehicle.
This configuration is used in braking a diesel-electric engine. To brake a diesel-electric engine, the traction motor, which is driven by the rotating wheels of the moving vehicle, becomes an electric power generator. The electricity from the traction motor is conducted to the braking grid. The braking grid includes a resistance element or elements made of a metallic material that is conductive, but provides resistance to the current received from the traction motor so that the current is converted to heat that is radiated from the resistance elements. Thus, the energy of motion of the locomotive engine, or other vehicle in which this configuration is installed, is converted to heat in the dynamic braking operation mode.
An issue that arises when dynamic braking systems are employed to brake a vehicle, such as a locomotive, traveling at high speed, or when the dynamic braking system is applied to a vehicle traveling downwardly on a relatively steep grade, is that the dynamic braking grid may overheat. Cooling fans typically are employed to direct cooling air over the resistance elements of a dynamic braking grid to maintain the temperature of the resistance elements below a temperature at which damage resistance elements or other components of the braking system might occur. Such fans typically are large in order to provide sufficient air movement uniformly over the entire area of the resistance element, and to utilize the electric power provided to the dynamic braking grid by the traction motors. Such motors also may be shielded to protect their internal components from high external temperatures and corrosive airborne particulates.
Systems of dynamic braking grids and cooling fans take up significant space in the engine compartment of a vehicle, or hood unit of a diesel-electric locomotive or other vehicle in which they are mounted. Accordingly, there is a need for a braking grid cooling system that effectively and efficiently dissipates heat generated by rheostatic braking, and is relatively compact in size.